Scalp Artery MRI Helps Detect Giant Cell Arteritis

Initial screening option to rule out biopsy need

Action Points

Note that this cross-sectional study comparing MRI with gold-standard temporal artery biopsy for diagnosis of giant cell arteritis (GCA) found that MRI had a high negative predictive value, but poor positive predictive value.

This suggests that, after external validation, MRI might be considered an initial screening test in patients suspected of having GCA.

A Canadian prospective cohort study inArthritis & Rheumatology found that a normal scalp artery MRI strongly correlated with a negative temporal artery biopsy. "This suggests that MRI could be used as the initial investigation in giant cell arteritis, temporal artery biopsy being reserved for patients with an abnormal MRI," wrote the research team led by Maxime Rhéaume, MD, of Sacre-Coeur Hospital in Montreal.

Abnormal MRI, however, was associated with either positive or negative biopsy among 171 patients tested for suspected giant cell arteritis. Temporal artery biopsy was positive in 31 patients (18.1%), while MRI was abnormal in 60 (35.1%).

This large vessel vasculitis affecting older individuals can be challenging to diagnose, Rhéaume and colleagues noted. The age- and sex-adjusted incidence rate per 100,000 population increases from 2.2 in the 50-to-59 age group to 51.9 in those over age 80.

The study -- which the researchers said is the first series of its kind -- involved 171 patients with a mean age of 70.6. Of these, 73.3% were women, with all patients treated at St. Joseph's Healthcare Center in Hamilton, Ont., during 2007 to 2014. The most frequent symptoms were headache (occurring in 84.2% of patients), visual changes (50.3%), and artery tenderness (47.7%). Jaw claudication was present in 28.1% of patients and vision loss in 19.3%.

Almost all the patients (92%) were already on glucocorticoid therapy when recruited for the study, with a mean duration of treatment at MRI of 8.5 ± 8.2 days (range 0-48) and at biopsy of 14.2 ± 10.6 days (range 1-60) at the time of temporal artery biopsy.

Patients underwent high-field 3 Tesla MRI of the scalp arteries followed by temporal artery biopsy, with a mean sample of 4 cm of arterial wall thickness and enhancement on multiplanar post-contrast T1-weighted spin-echo.

Images were graded according to a published severity scheme (scale of 0 to 3).

MRI was abnormal in 29 of 31 patients with a temporal artery positive biopsy, missing two who had been on glucocorticoid therapy. "There is data showing that MRI abnormalities are reduced within two weeks of introduction of glucocorticoids," the researchers wrote. "It is unclear whether exposure to glucocorticoids explains these two MRIs being negative, but MRI should be performed as quickly as possible to maximize sensitivity."

In 140 patients with a normal biopsy, 109 had a normal MRI. Hence, MRI had a sensitivity of 93.6% (95% CI 78.6-99.2) and a specificity of 77.9% (95% CI 70.1-84.4).

Among 111 patients with a normal MRI, 109 had a normal biopsy, giving MRI a negative predictive value of 98.2% (95% CI 93.6-99.8). Of the 60 patients with an abnormal MRI of the scalp arteries, 29 had an abnormal biopsy, yielding a positive predictive value of 48.3% (95% CI 35.2-61.6).

MRI found multiple vessels to be affected in 47 cases, with two patients showing isolated occipital artery involvement. On average, 4.1 ± 2.4 vessels were involved in abnormal-MRI participants.

As the authors pointed out, temporal artery biopsy is invasive and its true sensitivity is unknown, yet diagnostic accuracy in giant cell arteritis is crucial because of the potential for blindness with untreated disease and, conversely, the adverse side effects of glucocorticoid therapy.

It's important to get an early diagnosis and start treatment as soon as possible," agreed Robert Hylland, MD, of Michigan State University College of Osteopathic Medicine in Lansing, in comments to MedPage Today. "This study is interesting and exciting in terms of the possibility of earlier diagnosis, but it shows we still have to do a lot more work."

He said the investigation is "more of a gateway study showing us what we might further explore – for instance, what is the yield of this test in patients before they get put on prednisone? That is the next study that needs to be done, I think."

While Hylland found it encouraging that MRI picked up abnormalities in the occipital artery of one patient, he said it was concerning that the technique missed two biopsy-positive patients (they had been on glucocorticoid therapy). "Missed patients could have missed out on treatment and gone on to blindness," he said, but conceded that biopsy can also be negative -- "So oftentimes we rheumatologists will treat anyway based on clinical features and a good history."

MRI might be particularly useful for "iffy" patients, he added. "If an MRI angiogram is negative, that might be an indication in an uncertain case that it's not temporal arteritis, and you might go for a different diagnosis. We really do need earlier and easier diagnosis, and MRI might fit in well as the first wave of tests."

Rhéaume and colleagues noted that the high negative predictive value of MRI might have been due not only to the test's sensitivity, but also to the prevalence of arteritis in the study population: "A critical question for the generalizability of our results is whether our population is representative of patients undergoing a temporal artery biopsy."

The researchers called for multicenter validation of the results "to clarify the potentially very important role of MRI in the diagnosis of giant cell arteritis."

This study received no funding. Rhéaume's fellowship training was supported by Association des specialistes en medecine interne du Quebec and the Fondation de l'Hopital du Sacre-Coeur de Montreal, Quebec.

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